Heretofore, as the method for preparing pyrazolecarboxylic acid from alkylpyrazole derivatives, it has been known the permanganic acid oxidation method.
However, this method uses excessive amount of permanganate and the yield is extremely bad as 40% or lower.
Also, it is required to process a large amount of waste water and waste material containing manganese so that it is difficult to employ the method as an industrial scale preparation.
Also, as the preparative method of heterocyclic carboxylic acid due to the liquid phase autoxidation method, the following has been known.
(1) Japanese patent publication No. 9868/1959 PA0 (2) Japanese patent publication No. 17068/1975
In the aforesaid (1), oxidation of a compound having pyridine or quinoline nucleus has been carried out in the presence of a heavy metal compound such as manganese, cobalt, etc. and a bromine compound.
In the aforesaid (2), oxidation of alkylpyridine derivatives have been carried out in the presence of a compound selected from zirconium, cobalt and manganese and a bromine compound to prepare pyridinecarboxylic acids.
However, it has never been known the method in which only a methyl group of a pyrazole compound having simultaneously a methyl group bonded to the pyrazole ring and a substituent bonded to a nitrogen atom is selectively oxidized to give pyrazolecarboxylic acid derivatives.